Wait or fight? Ownership asymmetry affects contest behaviors in a parasitoid wasp

Abstract

Contests for indivisible resources are often settled on the basis of the asymmetry that exists between contestants in their ownership status: Owners (i.e., individuals already possessing a resource) usually retain the resource when facing intruder competitors. This owner advantage is predicted to be more pronounced as the asymmetry in ownership status accentuates: when the residency period increases, the probability of owners keeping their resource should increase and contestant aggressiveness should be reduced. In the present study, we tested this prediction in a parasitoid wasp, Eupelmus vuilleti, where females fight for hosts, larvae of Callosobruchus maculatus, on which to lay their eggs. To do so, we experimentally varied the arrival times of 2 conspecific females on a host, generating different asymmetries in ownership status between them. We further explored the strategies adopted by intruder females according to the stage reached by the owners in their host exploitation sequence. When the residency period was short, both females fought and contests were won by the female valuing more greatly the host, rather than by the owner per se. The loser left the host vicinity and the winner exploited the host alone. In contrast, when the residency period was long (the owners were ready to parasitize the host), the intruders did not leave but instead waited for the departure of the resident female in order to superparasitize the host. This “waiting strategy” seems particularly adaptive in this species, in which females tend to prefer already parasitized hosts to healthy hosts. Key words: contest resolution, Eupelmus vuilleti, female egg load, ownership status, resource value. [Behav Ecol]